Often it is necessary to attach mate-able fixtures between the device under test (DUT) and a vector network analyzer (VNA) in order to measure and characterize circuitry. These fixtures tend to electrically interfere with the measurements causing erroneous results.
To compensate for these errors, industry has adopted standards that utilize calibration structures and procedures to calibrate or de-embed out errors not compensated internally by the VNA. The most common calibration structures are Thru-Reflect-Match (LRM), Thru-Reflect-Reflect-Match (LRRM), Thru-Reflect-Line (TRL or LRL), Short-Open-Load-Thru (SOLT), and Short-Open-Load-Reciprocal (SOLR). Ideally, these structures may be used with any VNA and will effectively compensate all errors within the bandwidth of the fixtures and VNA.
In practice, not all calibration structures may be used with any VNA since the VNA should have the circuitry, programing algorithms, and user interfaces for each calibration structure. Therefore, many circuit designs and tests are limited by the capabilities of the VNA. Furthermore, the calibration procedures and structures do not characterize any of the limitations of the fixtures themselves, such as bandwidth, cross-talk, and insertion loss. Instead, these fundamental measurements are deferred to the fixture manufactures and may be available in the components data-sheet or manufactures website. Engineers should be aware of these fixture limitations. Otherwise no matter how accurate the calibration, the fixture limitations may invalidate the measurements.
De-embedding is another method that is utilized to characterize the DUT. De-embedding is a method of mathematically removing the parasitic interference from measurement fixtures. The exact structural embodiment of these fixtures varies from simplistic mating connectors, such as thin-wire-probes, to very complex networks, such as micro-traces, vias, striplines, wire-bonds, etc. The ability to mathematically remove these parasitic effects hinges on accurately characterizing the connected test fixtures. As such, current de-embedding methods rely almost exclusively on the aforementioned calibration standards to characterize test fixtures.